Optical sighting instrument with means for producing a sighting mark

ABSTRACT

An optical instrument comprising a lens means having a concave light reflecting surface serving as a semi-transparent mirror, and a light source for directing light beams to the semi-transparent mirror which is arranged to produce an image of the light source, such that said image to an observer who has his eye directed to the concave mirror surface appears to lie far in front of the mirror to serve as a sighting mark on a sighting line between the observer&#39;s eye and a target; the lens means with the semi-transparent concave mirror surface and the light source being arranged such in relation to each other and in relation to the sighting line that the optical main axis from the light source to the lens means intersects the sighting line substantially on the semi-transparent mirror surface and intersects the theoretical optical main axis of the lens means in a point situated close to the focus of the concave mirror surface, and such that the focus and said point are transversely spaced from the sighting line whereby sighting errors as a result of misalignment of the observer&#39;s eye in relation to said sighting line will be reduced to a minimum.

This invention relates to an optical sighting instrument which comprisesa lens means adapted to serve as a semi-transparent concave mirror, anda light source so arranged that the mirror gives to the observer's eyean image of the light source which serves as a sighting mark.

In an instrument of this kind which is known from French Pat. No.1,126,409 use is made, as a light source, of a fluorescent rod of glassor plastic which is adapted to have its circumference illuminated byambient light or by light from an auxiliary light source and is arrangedto emit light through its one end which is directed to the mirror. Bothends of the rod are silvered or otherwise closed to light emissionexcept for an aperture in the form of a reticle in the silver layer atthe end of the rod directed to the mirror, and the rod can be adjustedrelative to the mirror to allow placing the reticle in the focus of theconcave mirror surface.

With this instrument the mirror image of the light source will beperceived by the observer as a sighting mark situated at a greatdistance in front of the mirror and the observer will be able to movehis eye in a zone corresponding to the field of the mirror without anyparallax error occurring between the image of the reticle and the targetarea, which makes it possible to place a small filter between theobserver's eye and the target and to observe or aim at the targetoptionally through the filter or directly above or below the filter.

In order that no parallax error or double image shall arise the lightsource being reflected shall be a point or surface (one- ortwo-dimensional), i.e. all light shall appear as if it arrived from thereticle proper. This is not, however, the case in the previously knowninstrument described, for the light emitted from the reticle does notappear to come from one and the same plane, i.e. the plane of thereticle, but also from the rear end of the rod and from several pointswithin the rod proper. The rod is not either totally reflecting, for alllight rays within the rod that are incident to the peripheral surface ofthe rod at angles outside a total inner reflection, are emitted from therod with consequent weakening of the light.

The previously known instrument described suffers from two essentialdrawbacks, the first being that the light from the reticle does not seemto come, in its entirely, from the plane of the reticle, and the secondbeing that the light loss and thus the light weakening in the rod isrelatively large. If the marksman is, for instance, in the shade andaims at a target lighted by the sun, no sighting mark is obtained.

A further disadvantage is that the length of the optical system will berelatively large since this length also includes the whole length of theglass rod and that the glass rod cannot be exploited in any manner otherthan as part of the light source proper.

Moreover, it is previously known from Swedish Pat. application No. 12736/71 to provide a lens serving as a semi-transparent concave mirror,and a light source placed in the focus of the mirror, said parts beingso arranged that the main axis of the lens/mirror constitutes an axis ofsymmetry for the marksman's line of sight and a line between the lightsource and the centre of the lens. This device involves int.al. theimprovement that the light viewed in the mirror seems to come from asingle plane, whereby the picture of the light source, which isseemingly at a great distance in front of the mirror, can beconcentrated in a better way than in the device described above.However, in this case as in the device described above a certainperturbation of the image is caused by refractions in the two sides ofthe lens (double image) at a small focal distance.

The present invention has for its object to overcome these problems andto this end the optical sighting instrument according to the inventionincludes a monolithic or composite body shielded at the circumferenceand made of glass or optically equivalent material, which body has atits front end a concave surface of refraction facing the rear end of thebody and forming a semi-transparent concave mirror surface, and thelight source is arranged in conjunction with said body at a lightadmission surface situated at the rear end of the body or between saidend and the mirror surface, being located laterally of and at a distancefrom a line of sight which extends through the body from the rear to thefront end thereof through the mirror surface.

According to the invention, the inner total reflection of light from alight source is exploited in an effective way with the smallest possiblelight loss, and image perturbation is diminished in that the light raysneed not travel in the air between the lens/mirror and the light source.The light source can be built into the lens proper.

In the simplest case the trajectory of rays in the optical system takesplace in one and the same medium, i.e., through a body of uniformmaterial, such as glass or equivalent plastic, but the body may also beconstructed from two or more pieces of material which are interconnectedby any one of the methods well-known in optics. In the latter case, thebody may be a glass rod and a ground lens fixed to one or both ends ofthe rod.

Normally, the optical system may be so arranged as to be neithermagnifying nor diminishing, but the invention also permits arranging theoptical system in such a way that it gives a magnification and thus canreplace a telescope sight.

Owing to the insignificant loss of light in the optical system accordingto the invention (inner total reflection) it is possible to userelatively weak light sources. This means that the energy sources(generally batteries) will have a long life, and the use of so-calledbeta light, of the kind employed in night sights, as a light source inthe sighting instrument according to the invention, is highlyadvantageous. A beta light of this type is made up of a glass capsulewhich is coated internally with, for instance, phosphorus and is filledwith an activating gas such as tritium gas. Tritium which is an isotopeof hydrogen, emits beta particles (electrones) which, when they strikephosphorus, cause this material to emit light of the colourcharacteristic of phosphorus. These light sources do not emit anyharmful radiation, they can be made shock- and vibration-proof andcompletely protected against damage from external sources. Moreover,they can be very small in size, having for example diameters of fromabt. 1/2 mm and more and lengths from abt. 5 mm and more, depending uponthe light intensity desired.

In target shooting, with for instance air pistols, when shooting iscarried out at a fixed distance (10 meters), it is possible toeliminate, when the light source is located in focus, such errors asarise by parallel displacements of the sighting mark when the observermoves his eye. This elimination is realized by moving the light sourcecloser to the mirror, i.e., inside the focus, in proportion to thedecreasing range to the target. The sighting mark will lie absolutelyimmovable on the target even if the observer moves high eyeconsiderably.

By arranging the light source in such a way that the light directedtowards the mirror seems to come from a single point or surface, thecorrect location of the light source in or relative to the focus of themirror is easily determined, since the theoretical centre of the lightsource coincides with that of the light-emitting surface.

When a light source in the form of a glass rod with silvered ends andwith an aperture (reticle) in one silvered end is used, a correct imageof the reticle is only obtained if the sighting mark is observed in themiddle of the mirror. A not insignificant portion of the total lightcomes from the silvered rear end of the rod, but if the observer moveshis eye so that the sighting mark is observed at the edge of the mirrorno light is obtained from the silvered rear surface, but only from thatlight which is reflected from the circumferential surface of the rod.When the observer moves his eye the light will thus vary in intensityand the sighting mark will be blurred (magnified).

The invention will be more fully described hereinbelow with reference tothe accompanying drawing, in which:

FIG. 1 is a longitudinal sectional view of a sighting instrumentaccording to the invention which is built into a tube;

FIG. 2, on a larger scale, is a longitudinal section of the light sourceat the sighting instrument in FIG. 1;

FIG. 3 is a diagrammatic side elevational view of the light transmittingbody forming both the light transmission medium and the mirror/lens inthe sighting instrument according to the invention;

FIG. 4 is a view similar to FIG. 3 of a body of composite design;

FIG. 5 is a view of a possible cross-sectional shape of the body at alevel with the light source;

FIG. 6 is a modification of the lens systems in FIGS. 1, 3 and 4.

FIG. 7 is a simplification of the lens system in FIG. 6.

The main constituent parts of the sighting instrument illustrated inFIG. 1 comprise a lens 1 and a light source 2 disposed in a tube 3. Thelens 1 is a cylindrical or rod-shaped body of ordinary lens glass, plexiglass or equivalent material. The front end surface 4 thereof is convexand the rear end surface 5 thereof is concave. The line R from theconcave end surface 4 drawn through the crossing with a line of sight Sthrough the lens from the rear end of the tube 3 at 6, said line ofsight being parallel with the longitudinal axis of the lens, extendsthrough the light source 2 which is mounted in a recess in the rear endportion of the lens near the circumferential surface thereof. The lens 1is adjustably and elastically suspended together with the light source 2in the tube 3 by means of rubber elements 7, 8, one of which is in theshape of a conical rubber sleeve 7 which at its inner narrow end isfastened about the lens 1 by means of a ring 9 and which at its outerend is fixed to the inner side of the tube 3 near the outer end thereof.The other rubber element 8 is in the form of a disk which at its innerperiphery is clamped about the lens 1 by means of a ring 19 near therear end of the lens, the outer edge of said ring being fixed to theinner side of the lens. A set screw 12 is screwed into a holder 11 onthe tube wall and bears with its inner end against a shoulder on thecircumferential surface of the lens at a point in front of the centre ofthe lens. The rod 1 can by swung by means of the set screw 12 in theplane of FIG. 1. A similar set screw 12' may be arranged in a positionturned through 90° in relation to the set screw 12, for adjusting thefront end of the lens 1 in a longitudinal axial plane at right angles tothe plane of FIG. 1. The sighting aperture 6 at the rear end of the tube3 may be designed in any suitable manner, for instance as ahopper-shaped mouth, as in a telescope sight. The tube is preferablyclosed at the outer end by means of a glass disk 13. The glass disk 13may be replaced by an ocular, in which case the tube end 6 can beadjustable.

The outer end 4 of the rod 1, as already mentioned, is externallyconvex; the surface 4' serving as a mirror will then be concave. Asshown, the axis R from the mirror surface makes an angle with the lineof sight S through the tube 3, the focus of the mirror surface lying atthe lower edge of the rear end of the lens 1, for instance slightlyoutside the point where the light source 2 is placed. Magnification isobtained if the rear concave end surface 5 of the lens 1 has a radius ofcurvature greater than the surface 4. The optical axis of the surface 5is parallel with the axis R and the circumference of the lens is eithermatted or coated with a light-impermeable coating 14 of some suitablekind.

As shown in FIGS. 1 and 2 the light is supplied to the light source atthe sighting instrument in FIG. 1 by a small lamp 15, the filament 16 ofwhich is connected to a battery 17 (see FIG. 1) and which is enclosed ina glass bed, for example, a bed of acrylic glass 18 which is cast into abrass sleeve 19. The front end of the brass sleeve has an aperture whichis filled with glass forming a plug 20 the outer side of which ismatted. The outer end of the glass plug 20 thus forms a matt, luminoussurface which is directed to that point of the mirror surface 4' of thelens 1 which is passed by the line of sight S. As a result, a light spotcoming from a single surface will be obtained. The front end portion ofthe brass sleeve 19 is preferably placed in a recess in the rear end ofthe rod (as appears from FIG. 1 and as diagrammatically shown in FIG.3), but it can also be placed at the outer edge of the rear end of thelens 1.

It is also possible to provide a recess, in or near the rear end of thelens 1, which is shielded at the sides 21 (FIG. 3), which is matted atits bottom surface facing the middle of the mirror surface 4' (the pointis cut by the line R in FIG. 1), and which constitutes the light source2 in conjunction with the lamp 15 placed in the recess or sending itslight into it.

The lens 1 can be ground so that it has neither magnifying nordiminishing properties, but should a magnification be desired (ordiminution, which is less probable), this can easily be realized bysuitable grinding of the surfaces 4, 5. The desired optical propertiescan be realized by grinding of the ends of a glass or plastic rod ofsuitable cross-section and length, or by the use of a combination ofcomposite lenses, for instance two lenses 22, 23 at the ends of aplastic or glass rod 1' (FIG. 4).

In the embodiment according to FIG. 4 the rod 1' may consist of forexample lens glass or plexi glass and can have straight or obliquelyplane-ground ends 24, 25. In the case illustrated, the front lens 22 isa plane-convex lens and the rear lens 23 is a plane-concave lens. Themirror surface in this case is the rear 4' of the convex surface 4 ofthe plane-convex lens 22. The lamp 15 may be placed in the rear lens 23or adjacent to it near the circumference thereof, or may extend with itsfront end through said lens up to the rear end 25 of the rod 1', i.e.the surface which, in its capacity as light-emitting surface has beencalled the light source 2.

If it is desired to change the location of the light source 2 relativeto the focus of the mirror surface 4', the light source (for instancethat shown in FIG. 2) may be displaceable and adjustable into desiredpositions along the axis R of the mirror.

It should be observed that the lens 1 need not be circular-cylindrical.It may have, for instance, conical shape with circular cross-sectionalform or may have any other suitable shape which will provide more spacefor the light source, for example the pear-shaped cross-sectional formillustrated in FIG. 5. Moreover, the rod 1' can be combined with lensesof any suitable configuration for obtaining the desired opticalproperties. The combination of a body of glass or equivalent material,such as the rod 1' in FIG. 4, and lenses, such as 22, 23, can berealized according to methods well-known in optics for avoidingperturbation phenomena and errors of refraction. Preferably, use can bemade of Canada balsam (a resinous binder), to fix a lens at the end of arod 1'. This balsam has the well-known property of permitting thebonding of well-ground lens surfaces without giving rise to undesiredreflection.

In the sighting instrument according to the invention use is made of arod (single or composite) of glass or equivalent light-permeablematerial both as a mirror and as a light ray trajectory and in certaincases also as a magnifying lens. The circumference of the rod is mattedor otherwise shielded and the light penetrating through the rear end ofthe rod in the assembly according to FIG. 1 is insignificant relative tothe light from the light source 2, and is not capable of blurring thesighting mark, i.e. the image of the light source situated in front ofthe sighting instrument.

As shown in FIG. 6, it is conceivable to combine or to replace the rod 1or 1' with a composite lens system comprising two assembled (e.g. gluedtogether) lenses 4a, 4b, in which the boundary layer 4' between thelenses serves as a semi-transparent mirror for light from the lightsource. This can be realized by using lenses 4a, 4b of different indexesof refraction or by using a reflection layer between the lenses. A lenssystem combined according to this principle is neither magnifying nordiminishing. One lens 4a is formed so as to eliminate sphericalabberation from the reflecting surface 4' between the two lenses 4a, 4b,while the other lens 4b is formed in such a way that the lens system 4a,4b will be zero-refracting (neither magnifying nor diminishing) and willthereby compensate for the requisite deviation of the lens 4a fromzero-refraction necessary for abberation correction. The trajectory, inthe rod 1", of the rays from the light source is advantageous also inthis case, though not absolutely necessary to attain an absolutelyparallax-free lens system which allows the observer to move his eyewithout resulting sighting errors.

In this case the rod 1" may be omitted, whereby the lens 4a takes overthe function of this rod 1".

In a further modification, however, the lens 4a may be omitted, in whichcase the rod 1" will be formed to eliminate spherical abberation fromthe reflecting surface 4' between the lens 4b and the lens formed by therod 1" in FIG. 6. Also in this case the lens 4b is formed such that thelens system 4b, 1" will be zero-refracting, e.g. such that the lens 4bwill compensate for the requisite deviation of the lens 1" fromzero-refraction.

In FIG. 6 (as in FIG. 1) the light source 15 is positioned such that thelight emitting surface 2 is situated in the focus of thesemi-transparent mirror surface 4', and such that the optical axis R ofthe light emitting surface 2 is situated between the line of sight S anda line between the light surface 2 and the centre point C of the lenssystem 4a, 4b; this point C is situated at or close to the lower edge ofthe lens system 4a, 4b (the lens system 4a, 4b is formed such that itmay be considered cut from a sector of a symmetrical lens with thecentre C in its middle point).

The light source, i.e. the luminous surface 2, may be in the form of acircular surface, a cross, a T or in any other suitable form normallyused for sighting marks. The essential thing is that the light source isarranged in such a way that the light seemingly comes from one and thesame surface which is planar or which may be curved, with all points ofthe luminous surface being equidistant from the mirror surface. Therequirement that the image be sharp and the light loss as small aspossible is satisfied with the embodiment according to the invention.

As mentioned in the introduction, use can be made, as a light-generatingelement, of so-called beta light comprising a glass capsule which isinternally coated with, for instance, phosphorus and is filled with anactivating gas such as tritium gas. A light-generating element of thistype may be of very small dimensions and may therefore be easily mounted(exchangeably) in the glass body proper of the sighting instrumentaccording to the invention. A light-generating element of this kind canbe mounted for instance in the location of the lamp 15 in FIG. 4 anddoes not require any connections to a battery. A beta light is extremelywell suited for shooting in the dark and is, besides, used for thispurpose in conventional night sights.

Thus beta light has great advantages which can be exploited, in a novelmanner, in the sighting instrument according to the invention but betalight also has the disadvantage that the light intensity cannot bevaried as simply as in a battery-driven lamp, the light intensity ofwhich can be varied by adjustment of a resistor. However, use can bemade of relatively intensive beta light in combination with insertibleor exchangeable filters for great or small subduing of the lightintensity emitted.

In a preferred modification, use is made of a light source in the formof a light emitting diode 15, where the light source proper or, asshown, the outer end 2 of a rod 15' of a light leading material, such asacrylic plastic, is connected with the diode to serve as a lightemitter. This light emitting diode or rod 15' may be arranged such thatit will have a laser effect, e.g. such that the light beam from thelight source to the surface 4' is sharply confined. Diodes of smalldimensions and having the desirable characteristics mentioned above aswell as the desirable characteristic of consuming very low electricpower are -- or are supposed in a near future to be -- available on themarket and are considered to be well suited for use as light sources insighting instruments according to the invention.

It will appear from the above that the primary parts of the sightinginstrument according to the invention, i.e. the lens or lens assembly 1having a semi-transparent mirror and the light source 2 can be modifiedin many ways, and that it is very simple to amount these parts of thecompact sighting instrument adjustably in a housing of some kind, forinstance the tube 3 shown in FIG. 1, especially when said parts 1, 2 arecombined as shown in FIGS. 1, 3, 5 and 6 but also when these parts 1, 2are spaced from each other as in the modification explained inconjunction with the description of FIG. 6. It is also pointed out, andshown in FIG. 7, that the centre C of the lens system may be situated ata point outwardly of the periphery of the lenses proper, e.g. spaceddownwardly from the lower edge of the lenses as in FIG. 7, wherereference numerals identical with those in FIGS. 1, 4 and 6 stand foridentical or substantially equivalent parts. The lenses in FIG. 7 as inFIGS. 1, 3, 4 and 6 are supposed to be cut from symmetrical lenses,having a centre C in the middle point, in an area between the peripherythereof and a line which is a tangent to said periphery and is spacedfrom the centre of said supposed symmetrical lens. Also in this case anybeam R from the light emitting surface 2 to the reflecting surface 4'will be reflected back as a light beam along or parallel with the sightline S and with the beam or line R situated between the line S (or anybeam parallel therewith) and a line extending from the light emittingsurface 2 to the lens centre C (which may be situated at or near or evenoutwardly of the lower edge of the lens or lens system). Under thesecircumstances a very quick aiming of a weapon equipped with theinstrument according to this invention will be possible. As soon as theuser's eye sees the sighting mark on the target the sighting mark willbe coincident with the point of impact of the weapon without anyparallax.

What I claim as new and desire to secure by Letters Patent is:
 1. Asighting instrument having front and rear ends and comprising a lensmeans mounted at said front end of the instrument and including asemi-transparent concave mirror surface facing said rear end of theinstrument to be viewed therefrom and having its axis directed such thatthe focus of said concave mirror surface is offset from the sightingline of said instrument, and a light source having a light emittingsurface positioned substantially at the focus of said concave mirrorsurface for directing light onto said concave mirror surface to producea confined image of said light emitting surface, which is useful as asighting mark and which to an observer who has his eye directed to saidmirror surface in a distance rearwardly thereof, appears to lie in frontof the mirror on the sighting line between the observer's eye and atarget, said lens means with said concave mirror surface and said lightsource being arranged such in relation to each other and to saidsighting line that the main axis of light emitted from said lightemitting surface intersects said sighting line substantially on saidsemi-transparent mirror surface and intersects the theoretical opticalmain axis of said lens means in a point close to the focus of theconcave side of the mirror surface, wherein said lens means comprises afront lens and a rear lens with said semi-transparent mirror surfacearranged between said lenses, said rear lens being formed to eliminatespherical aberration from the reflecting semi-transparent mirror surfacebetween said lenses and said front lens being formed such that the lenssystem will be zero-refracting, and wherein said light source placedsubstantially at the focus of said mirror comprises a light emittingdiode adjustably movable in relation to said focus and a body of opticalmaterial extending from the front end of said diode and providing withits front end said light emitting surface of a configuration to producesaid confined image useful as a sighting mark.
 2. An instrument asclaimed in claim 1, wherein said lens means is so designed that itstheoretical optical axis is spaced from and parallel with said sightingline.
 3. An instrument as claimed in claim 1, wherein said lens meanscomprises a body of optic material extending from said light emittingsurface and wherein said light emitting surface is provided in a recessin said body.
 4. An instrument as claimed in claim 1 wherein the lightemitting surface is a matted surface.
 5. An instrument as claimed inclaim 1, wherein said light emitting surface is an end surface on anelongated body having a light leading capacity of the linearcharacteristic of acrylic plastic.
 6. An instrument as claimed in claim1, wherein a body of acrylic plastic extends from said light emittingsurface to said lens means.
 7. An instrument as claimed in claim 1,wherein the rear end of the lens means is of a shape substantiallycorresponding to that of the mirror surface, and has an axis parallel tothat of the mirror surface.
 8. An instrument as claimed in claim 7,wherein a body of optic material is fixed at the rear end of said frontlens to serve as said rear lens.
 9. An instrument as claimed in claim 1,wherein said lens means comprises a rod-shaped body of optic materialwhich together with the lens means constitutes a unit extendingrearwardly to and contacting said light emitting surface.
 10. Aninstrument as claimed in claim 9, wherein said light source is at leastpartially mounted in a rear end portion of said body.
 11. An instrumentas claimed in claim 9, wherein said body in its rear end portion has acylindrical recess having a bottom surface and an axis directed to themirror and extending at right angles through said bottom surface andwherein said light emitting surface is positioned close to said bottomsurface.
 12. An instrument as claimed in claim 1, wherein said lightsource is a light source having a laser effect.
 13. An instrument asclaimed in claim 1, wherein said lens means and said light source areadjustably mounted and elastically suspended in a tube of substantiallythe same shape and configuration as that of a telescope sight.
 14. Asighting instrument having front and rear ends and including a lensmeans mounted at said front end of the instrument and including asemi-transparent concave mirror surface facing said rear end of theinstrument to be viewed therefrom and having its axis directed such thatthe focus of said concave mirror surface is offset from the sightingline of said instrument, and a light source having a light emittingsurface positioned substantially at the focus of said concave mirrorsurface for directing light onto said concave mirror surface to producea confined image of said light emitting surface, which is useful as asighting mark and which to an observer who has his eye directed to saidmirror surface in a distance rearwardly thereof, appears to lie in frontof the mirror on the sighting line between the observer's eye and atarget, said lens means with said concave mirror surface and said lightsource being arranged such in relation to each other and to saidsighting line that the main axis of light emitted from said lightemitting surface intersects said sighting line substantially on saidsemi-transparent mirror surface and intersects the theoretical opticalmain axis of said means in a point close to the focus of the concaveside of the mirror surface, wherein said lens means includes a frontlens and a rear lens with said semi-transparent mirror surface arrangedbetween said lenses, said rear lens being formed to eliminate sphericalaberration from the relecting semi-transparent mirror surface betweensaid lenses and said front lens being formed such that the lens systemwill be zero-refracting, and wherein said light source comprises acapsule containing a medium emitting beta particles and a substancearranged to receive and adapted to be activated by said particles toemit a light characteristic of the substance in question, said capsulehaving a front end closed by optic material the front end of whichprovides said light emitting surface of a configuration to produce saidconfined image useful as a sighting mark.
 15. An instrument as claimedin claim 14, wherein said medium being tritium gas and said substancebeing phosphorus.